Ashok Kumar Bhattacharya

Catalytic studies on ceria lanthana solid solutions III. Surface segregation and solid state studies

Abstract As part of a catalytic study, the bulk structure and surface compositions of the mixed oxides of ceria and lanthana, Ce 1− x La x O 2− x /2 , have been studied over the entire range of compositions. Between x =0 and x =0.6, the system forms solid solutions with the cubic fluorite structure. Beyond x =0.9, it forms solid solutions with the hexagonal close-packed structure characteristic of lanthana. No phase characterisation was possible between x =0.6 and x =0.9. Lanthanum is preferentially segregated at the surface from bulk compositions up to x =0.9, but further increments of lanthana cause the system to exhibit preferential surface segregation of the cerium moiety. The preparative procedure is shown to establish stationary state surface compositions, enabling classification of the composition data as segregation isotherms. Over the composition ranges of the two solid solutions, that is, x =0–0.6 and x =0.9–1, the surface segregation may be quantitatively described by power laws similar to the Freundlich gas adsorption isotherm.

Catalytic studies on ceria lanthana solid solutions II. Oxidation of carbon monoxide

The catalytic combustion of carbon monoxide over ceria, lanthana, and their mixed oxides has been studied under reaction conditions free from heat and mass transfer limitations. The bulk structures, surface compositions, and surface areas of the catalysts were determined by XRD, XPS, and BET methods, respectively. Doping either ceria or lanthana with low levels of the other oxide retards the reaction. The reaction order on carbon monoxide is almost first-order over ceria, but over the lanthana-containing catalysts it changes from positive to negative with increasing partial pressure. With all catalysts, the rate tends to zeroth order on oxygen with increasing partial pressure. An extended study was made of the major solid solution, lanthana-in-ceria, which operated near-threshold temperatures is poisoned by lanthana. The active centres are ensembles of cerium atoms, the size being lowered by lanthanum. The retardation is discussed in terms of interactions between cerium ensembles and anionic vacancies.

Catalytic studies on ceria lanthana solid solutions I. Oxidation of methane

Abstract The catalytic combustion of methane over ceria, lanthana, and the entire range of mixed oxides has been studied under reaction conditions free from limitations set by the transfer of heat and mass. Bulk structures of the catalysts were determined by X-ray diffraction and their surface compositions were monitored by XPS. Their surface areas were measured by BET methodology. Surface basicity was measured by temperature-programmed desorption of carbon dioxide. The combustion rate was close to first order on methane partial pressure, close to zeroeth order on oxygen partial pressure, and strongly retarded by carbon dioxide. A particular study was made of the solid solutions of lanthana in ceria where, operated at temperatures just above that of threshold activity, the two metal oxides act synergistically in the catalytic combustion of methane. It is proposed that cerium and lanthanum interact to form the catalytic active centre providing both redox and base functions.

3D Modelling of Biological Systems for Biomimetics

With the advanced development of computer-based enabling technologies, many engineering, medical, biology, chemistry, physics and food science etc have developed to the unprecedented levels, which lead to many research and development interests in various multi-discipline areas. Among them, biomimetics is one of the most promising and attractive branches of study. Biomimetics is a branch of study that uses biological systems as a model to develop synthetic systems. To learn from nature, one of the fundamental issues is to understand the natural systems such animals, insects, plants and human beings etc. The geometrical characterization and representation of natural systems is an important fundamental work for biomimetics research. 3D modeling plays a key role in the geometrical characterization and representation, especially in computer graphical visualization. This paper firstly presents the typical procedure of 3D modelling methods and then reviews the previous work of 3D geometrical modelling techniques and systems developed for industrial, medical and animation applications. Especially the paper discusses the problems associated with the existing techniques and systems when they are applied to 3D modelling of biological systems. Based upon the discussions, the paper proposes some areas of research interests in 3D modelling of biological systems and for Biomimetics.